Combined zirconium,aluminum and chrome tannage

ABSTRACT

In a process for tanning and re-tanning hides, pelts, e.g pickled pelts having a pH between 2.0 and 3.5, wool-skins, fur-skins and leathers, they are treated with a tanning agent comprising zirconium, aluminium and chromium salts, the proportion of these salts, computed as the proportion of the oxides ZrO2:Al2O3:Cr2O3, bein 100: 5-50: 2-30, preferably 100: 10-20: 3-8, by weight. The tanning agent may be a mixed complex of Zr, Al and Cr salts obtained by heating and/or dehydrating, e.g. evaporating, spray-drying or roller-drying, an aqueous solution containing them.  According to Example 1, a powdered Al-Cr mixed complex is prepared and mixed with aqueous, technical zirconium sulphate, the mixture is heated to 80 DEG  C., then cooled and spray-dried to yield a powdered tanning agent, in which the proportion of the oxides ZrO2:Al2O3: Cr2O3 is 100: 14: 7. Tanning may be effected first with a zirconium salt, and then with aluminium and chromium salts, e.g. in the form of a mixed Al-Cr complex described in French Specification 1,244,477.  The tanning agent may be in the form of an aqueous paste, a highly concentrated aqueous solution, or a powder.  Specified zirconium salts are: zirconium sulphate, e.g. containing finely divided silica gel, and zirconium oxychloride containing sodium sulphate. Specified aluminium salts are the sulphate, chloride and acetate. Specified chromium salts are the sulphate, nitrate, chloride, acetate and formate, and chrome alum. The tanning agent may also comprise one or more of the following acids and their sodium salts: sulphuric, phthalic, sulphophthalic, sulphosuccinic, tartaric, formic, acetic, lactic, glycollic and citric.  Resulting leathers may be re-tanned or after-treated with a mineral, vegetable, synthetic or resinous tanning agent, then dyed, fatliquored, filled and dried.  A suitable synthetic re-tanning agent is described in U.K. Specification 443,967. The following types of leather may be prepared using the process according to the invention: full grain leather, suede leather, nubuk, white or dyed glove leather, white splits, white belt leather, sole leather, aniline dyed kid leather and shrunk leather.

United States Patent Germany No Drawing. Filed Mar. 21, 1966, Ser. No. 535,721

Claims priority, applicatiogr 6(ielrmany, Mar. 26, 1965,

4 US. or. 8-94.25 12 Claims Int. Cl. C14c 3/06 White leathers which are an important material for the leather manufacturing industries are still predominantly produced by combining a chrome tanning and a tanning with svnthetic tanning agents which are more or less fast to light. However, these leathers do not satisfy the demands with regard to the white tint of the surface and the cut, the fastness to light and the dyeing and finishing properties. They must therefore be coated with a fairly thick layer of finishing agents, and this impairs their natural appearance which is at present regarded as an important argument in the competition with leather substitutes; there is also the risk that the dressing may give reason for complaints, especially at low temperatures.

Leathers, which are pure white and fast to light including the cut, can be obtained by means of aluminum or zirconium compounds, but compared with chrome-tanned leathers, these leathers have certain disadvantages during processing and also as finished products; they have, therefore, been accepted only to a limited extent and for special purposes, even when aftertreated with suitable synthetic tanning agents, fillers and fat-liquoring agents.

The leather treated with aluminum compounds is harder, less plump, less elastic and resilient than chrometanned leather, it presents more difficulties for dyeing, dressing and processing and is substantially less serviceable. Tanning with zirconium has brought a substantial advance in the production of pure white leathers, but these are still not wholly satisfactory in some important respects. Zirconium-tanned leathers are still too firm or not sufficiently elastic and they are not so easily fat-liquored and processed.

It has now been found that the disadvantages of the known tawing methods can be obviated to a considerably extent and that substantially more valuable, pure white leathers can be produced in a simpler manner, when hides or leathers are tanned with a combination of zirconium, aluminum, and chromium salts, the proportion of these metal salts, referred to the metal oxides being 100:5 to 50:2 to 30 parts by weight, preferably 100: to :30 to 8 parts by weight.

According to the present process, the zirconium, aluminum and chromium salts can be used either separately in any desired sequence or in the form of a mixture, but it is advisable to apply first the zirconium salt and subsequently the aluminum and chromium salts. It is also advantageous to use one of the three stated metal salts by itself and the other two metal salts in a mixture or in the form of a mixed complex by applying, for example, first the zirconium salt and then a mixture or a mixed complex of the aluminum and chromium salts. A preferred and particularly advantageous method of carrying out the tanning process according to the invention consists in using a mixed complex of zirconium, aluminum and chromium salts, as can be obtained, for example, by heating and/or dehydrating the aqueous solutions, for example by the heating of concentrated solutions, evaporation and/or spray-drying or roller-drying.

The preferred metal salts of zirconium, aluminum, and chromium are the sulphates. As zirconium sulphates, there may also be used, inter alia, technical zirconium sulphates which may contain finely divided silica gel. Zirconium sulphate or the corresponding ions can also be obtained during the tanning process by using zirconium oxychloride in the presence of sodium sulphate.

Besides aluminum sulphate, other aluminum salts may also be used, for example aluminum chloride and aluminum acetate. Besides chromium sulphate, there may also be employed, inter alia, chromium nitrate, chromic chloride, chromium acetate, chromium formate, chrome alum and the like.

The salts of zirconium, aluminum, and chromium may obviously also be used in complex form, for example, in the form of the known complexes of chromium and aluminum with organic and inorganic acids.

The zirconium, aluminum, and chromium salts are present in the ranges of basicity customary for tanning purposes. In addition to these salts there may be used nontanning inorganic or organic salts and acids, as are commonly employed in the tanning industry, e.g., sodium sulphate, sodium sulphophthalate, sodium phthalate, sodium sulphosuccinate, sodium tartrate, as well as the acids from which these salts are derived, such as formic acid, acetic acid, phthalic acid, sulphophthalic acid, lactic acid, glycollic acid, sulphosuccinic acid, and citric acid.

Mixed complexes of the three stated metals are obtained in a particularly simple manner, as already mentioned, by the spray-drying of aqueous solutions of the salts which are adjusted in accordance with the stated proportions, calculated on metal oxide. Similar good results are obtained by strongly or completely evaporating such solutions, the mixed complexes being thus obtained in a concentrated solution or in the dry form.

If mixed complexes of aluminum and chromium salts are used, which are preferably applied to a leather already pretanned with zirconium salts, the compounds described in French patent specification No. 1,244,477 are suitable, for example.

The zirconium, aluminum, and chromium salts acting as tanning agents are preferably used in the form of highly concentrated solutions or in the form of powders, tanning without a liquor being of particular advantage.

The term tanning without a liquor in the meaning of the present invention comprises tanning processes in which the tanning agents are used without water or without substantial amounts of water.

Tanning can also be performed with not so highly concentrated solutions, especially in the case of lighter leathers; the tanning through then proceeds more slowly.

The tanning process itself is chiefly carried out by milling the pelts or leathers with the tanning agents in a rotating drum.

In particular, the tanning can be performed in such a manner that pickled pelts the final pH value of which preferably lies between 2.0 and 3.5, are treated, after removal of the liquor, with a highly concentrated solution or a powder of a mixed complex of zirconium, aluminum, and chromium salts of the composition stated above, until they are completely tanned through, and the resultant leathers are deacidified and worked up in the usual manner. Instead of using the mixed complex of the said metal salts, the tanning can also be carried out first .with a zirconium salt in concentrated or powdered form and subsequently continued in any desired sequence, but preferably first with an aluminum salt and then with a chromium salt or also with a mixed complex of these two metal salts. In all these cases the sulphates of zirconium, aluminum, and chromium are preferred.

The use of a combination of zirconium, aluminum, and chromium salts offers many advantages over the known tanning with one of these salts by itself or with a mixture of two of these salts. The effects obtained in respect of resistance to hot water, whiteness, feel, plumpness, elasticity, grain firmness and fineness of grain have hitherto not been achieved by purely mineral tanning, while the wearing properties of the leathers is improved. In order to achieve the best possible effect on the properties of the leather, it is decisive that the proportion between the zirconium, aluminum, and chromium salts, referred to the metal oxides, ZrO :Al O :Cr O amounts to 100:5 to 50:2 to 30, preferably to 100:10 to 20:3 to 8 parts by weight.

A special advantage of using mixed complexes of the three stated metal salts, especially of the sulphates, such as are obtained by spray-drying or normal evaporation of the aqueous solutions, com ared with the use of a purely mechanical mixture, consists in that the tanning proceeds even faster and more uniformly. This leads to the assumption that the mixed complexes of the zirconium, aluminum and chromium salts in the stated proportions, referred to the metal oxides, are novel, previously unknown compounds with surprisingly valuable tanning properties. The use of such mixed complexes is a particular advantageous method of carrying out the process of the invention, but does not constitute any limitation thereof.

The new process also permits the rapid tanning through of very thick hide materials. The tanning combination of salts of the three metals is completely absorbed by the hide material so that the finished leather may have a very high total oxide content of over 13%, depending on the amount used for tanning, and exhibit a corresponding plumpness and compactness of the fibre structure, while remaining soft and elastic.

Hides of any thickness can be worked up according to the new process in a short time to produce the corresponding type of leather from glove leather to heavy upper leather, harness, belting and sole leather, and the additional use of other mineral, synthetic, vegetable or resin tanning agents and of fillers of organic or inorganic nature is also possible.

Instead of treating hides which have not yet been tanned, it is also possible to retan pretanned leathers, particularly chrome leathers, with the combination of salts of zirconium, aluminum, and chromium, marked effects being thus achieved in respect of more compact fibres, a firmer and finer grain and improved bufiing and finishing properties. The combination of zirconium, aluminum, and chromium salts can also be used in the dyeing of aniline leather as well as of sude and nubuk leather before, during or after the dyeing process; in this way dyeing effects are achieved in addition to the abovementioned tanning effect on the fibre itself. Deeper, bloomy, bright and level dyeings of improved fixation are thus obtained.

The following examples are given for the purpose of illustrating the invention.

EXAMPLE 1 Production of white calf leather (full grain upper leather, sude leather, nubuk) Calf pelts are pickled in the usual manner with sodium chloride and sulphuric acid so that the final pH is between 2.7 and 3.2. The liquor is then discharged and 18% (referred to the pelt weight) of the tanning agent described below are added through the drum door in powdered form by sprinkling over the pelts or pasted with water about 1:1. The drum is then allowed to run for 2-3 hours until the tanning through is complete. After shaving, the leather is deacidified with calcium formate and sodium bicarbonate or other conventional neutralising agents in a short liquor, until a level blue-green to blue coloration of the leather cut is achieved with gromocresol green, it is then fat-liquored with 36% pure fat calculated as pure fat content in the form of fat-liquoring products commonly used for the fat-liquoring of white leather, and dried.

Tanning agent: 800 parts of a technical zirconium sulphate containing 25% ZrO about 1 mol silicic acid and about 1 mol sodium sulphate per mol ZrO and having a basicity of about 45%, are mixed with 200 parts of an aluminum-chromium complex compound obtained according to the instruction given below, stirred with water in a ratio of 1:2 and heated to C. Heating of the solution is continued at 80 C. for about 15 minutes, and the reaction mixture is subsequently cooled to 40 C. and spray-dried. The powder thus obtained contains the metal oxides in the following proportion: parts ZrO 14 parts M 0 27 parts Cr O Preparation of the Al-Cr mixed complex: A mixture of 17 parts technical aluminum sulphate (Al (SO -18H O) and 7 parts of a chromic sulphate lye with a basicity of 33% and a Cr O content of 18%, dissolved with heating in 15 parts water, is adjusted by the addition of 4 parts calcined sodium carbonate in 13 parts water to a total basicity of 50%. One part anhydrous sodium acetate in 2 parts water is added to this mixture at a temperature of 50 C. The mixed complex compound formed after a reaction time of about 5 hours is dried by the spraydrying method. The powdered product contains about A1203 and Cr203- EXAMPLE 2 Production of white cow leather (full grain upper leather, suede leather, nubuk) Cow pelts are tanned as described in Example 1 with the tanning agent described below. After shaving, the leather is deacidified and retanned with calcium formate and sodium bicarbonate with the addition of about 3% (referred to the shaved weight) of a syntan (condensation product from 1 mol dihydroxydiphenylsulphone, 2 to 2.5 mols formaldehyde and 1 to 1.25 mols sodium sulphite) and fat-liquored, as described in Example 1.

Tanning agent: 100 parts of a technical zirconium sulphate containing 23% ZrO and about 1 mol silicic acid and about 1 mol sodium sulphate per mol ZrO and having a basicity of about 10%, are stirred with about 200 parts water and mixed with an aqueous solution of 21.5 parts of a technical aluminum sulphate (with 15% A1 0 and 8.9 parts of a technical chromic sulphate lye (with 18% Cr O and a basicity of 33%) in about 30 parts water. This mixture is heated at 80 C. for 15 minutes, cooled and dried by the spray-drying method. The resultant powder contains the metal oxides in the following proportion: 100 parts ZrO :14 parts Al O :7 parts CI2O3.

EXAMPLE 3 Production of white or dyed sheep leather (for full grain leather and sude leather) Patras sheep skins which are prepared in the normal way and thoroughly degreased are pickled with sodium chloride, calcium formate and sulphuric acid in the usual manner so that the final pH is between 2.7 and 3.2. The pickling liquor is then discharged and 12% (referred to the pelt weight) of the technical zirconium sulphate described in Examples 1 and 2 are added through the drum door in powdered form by sprinkling over the hides or pasted with water about 1:1, and the pelts are drummed for about 2 hours until completely tanned through. After brief rinsing of the leather, the liquor is thoroughly discharged, and 3% of the aluminum-chromium mixed complex described in Example 1 are added through the drum door, again in powdered form. The amount of metal oxides used for the tanning corresponds to a ratio of 100 parts ZrO 14 parts Al O :7 parts C 0 After drumming for 1 to 2 minutes, 2.5% of a commercial cation-active fat-liquoring agent are added through the hollow shaft of the drum, and drumming is continued for 90 minutes.

After shaving, the leather thus obtained is deacidified and retanned with calcium formate and sodium bicarbonate with the addition of about 4% (referred to the shaved weight) of, for example, the syntan mentioned in Example 2 as described in Example 1, and subsequently fat-liquored with 4 to 6% pure fat in the form of fat-liquoring products commonly used for white leather with the addition of wheat flour and kaolin or titanium dioxide pigment, and then dried. The leather to be dyed is deacidified without the addition of synthetic tanning agents and subsequently dyed, fat-liquored and dried in the usual manner.

The leathers obtained according to Examples 1 to 3 are characterised by their white colour and the great compactness of the fibre, in addition to good softness, plumpness and excellent tear resistance.

EXAMPLE 4 Production of white or dyed sheep leather from pickled sheep skins (for full grain and sude leather) [In this case the assumed pelt weight is the pickled weight plus 25%] Pickled sheep skins are depickled in the usual manner, degreased and repickled by means of sodium chloride, calcium formate and sulphuric acid. The pH value of the residual liquor is between 2.7 and 3.2. The pelts are then tanned with 9.4% of a technically pure zirconium sulphate containing 32% ZrO but no silicic acid, and having a basicity of about 45 to 50%, deacidified, retanned or dyed and fat-liquored as described in Example 3. Instead of 3% of the Al-Cr mixed complex used in Example 3, there is employed a mixture of a technical aluminum chloride with a content of 22% A1 and a basicity of about 65% and a technical chromic sulphate with a content of 25% Cr O and a basicity of 33%. The amount employed of the first compound corresponds to 0.54% Al O that of the second compound to 0.21% Cr O referred to the pelt weight), so that the ratio of the metal oxide combination is as 100 parts ZrO 18 parts Al O :7 parts Cr O The leather thus obtained is characterised by good grain firmness of the plumpness, feel and tear resistance.

EXAMPLE 5 Production of white or dyed glove leather Kid pelts prepared for glove leather in the usual manner are pickled, tanned, deacidified, optionally dyed, fat-liquored and dried as described in Example 1. The leather to be dyed is also wetted back in the usual manner after drying, then dyed, again fat-liquored, dried and dressed in conventional manner. The white leather is characterised by its whiteness, extraordinary plumpness and good handle, the dyed leather by its high brilliancy, good fastness to light and very good general fastness properties.

EXAMPLE 6 Production of white splits Split pelts are pickled with sodium chloride, calcium formate and sulphuric acid. The final pH of the liquor is between 2.5 and 3. The liquor is discharged and the following mixture is added in powdered form by sprinkling over the pelts:

7.5% of a technically pure zirconium sulphate containing 32% ZrO and having a basicity of 45 to 50%, but no content of silicic acid, are mixed with 5.4% of a technical aluminum chloride containing 22% A1 0 and having a basicity of about 65% and With 2.6% of technical chrome sulphate containing 25% Cr O and having a basicity of 33 This mixture corresponds to the following proportion of the metal oxides: 100 parts ZrO :50 parts Al O :27 parts Cr O After an operating time of 1 to 2 minutes, 3% of a commercial cation-active fat-liquoring agent are added.

When tanned through, the splits are deacidified as described in Example 1 by means of calcium formate and sodium bicarbonate, and fat-liquored in the conventional manner with the addition of white pigments. The splits thus obtained are characterised by their whiteness, good feel and excellent tear resistance.

EXAMPLE 7 Production of white belt leather Cow neck pelts of about 4.5 mm. thickness which have been prepared in the conventional manner are pickled' with sodium chloride, calcium formate and sulphuric acid so that the final pH is between 2.7 and 3. Tanning is carried out with 15% of the tanning agent described in Example 2, the amount of metal oxides employed being so chosen that ratio of parts ZrO :30 parts Al O :8 parts Cr O is obtained in the tanning agent. Tanning through is achieved within about 2.5 to 3 hours. The leather is then neutralised and retanned with calcium formate and sodium bicarbonate with the addition of 5% (referred to the shaved weight) of a commercial cyntan as described in Example 1, fat-liquored in the usual manner with the addition of white pigments, and dried in a slightly stretched state. The leather thus obtained is characterised by a very good whiteness, compactness of fibre, grain firmness dressing property.

EXAMPLE 8 Production of sole leather Cow butt pelts 5 to 6 mm. thickness prepared in the manner customary for this type of leather, are pickled with sodium chloride and sulphuric acid in the usual manner so that the final pH is between 2.5 and 3. The pelts must be thoroughly pickled, and this takes several hours. Tanning is subsequently carried out with 18% of the tanning agent described in Example 2. About 3-4 hours are required for tanning through. The leather is then levelled in the conventional manner, neutralised with calcium formate and sodium bircarbon-ate as described in Example 1, sammed and retanned in a drying drum with about 20% (referred to the samrned weight of the leather) of a sulphited quebracho extract in powdered form with the addition of the conventional fillers and fatlrquoring agents, dressed and dried. The leather thus obtained is characterised by a pale level shade, compact fibre structure and extraordinary resistance to abrasion.

EXAMPLE 9 Production of s-ole leather The treatment is carried out in the manner described in Example 8. Instead of quebracho extract, there is used a synthetic tanning agent, for example, a tanning agent described in German patent specification No. 675,775, or a mixture of both tanning agents.

EXAMPLE 10 Production of calf sude leather The calf skins chrome-tanned in the conventional manner are retanned with 3% (referred to the shaved weight) of the tanning agent described in Example 1 in powdered form and in a short liquor, neutralised and further processed in the usual manner to sude leather, with or without an intermediate drying of the skins before dyeing.

EXAMPLE 11 Production of sheep sude leather Chrome-tanned goat skins prepared in the manner customary for nappa leather are retanned with 6% (referred to the shaved weight) of the tanning agent desoribed in Example 1 in powdered form and with the addition of about 3% of a cation-active fat-liquoring agent, neutralised and further processed to sude leather in the usual manner.

7 EXAMPLE 12 Production of sude and nubuk leather (cow, calf, goat and sheep leather) The leather prepared and chrome-tanned in the conventional manner is further treated in the usual Way, 3% (referred to the shaved Weight, 6% referred to the dry weight) on the tanning agent described in Example 1 being used in powdered form during the dyeing, optionally with the addition of cationic fat-liquoring agent, between two additions of dyestuif.

EXAMPLE 13 Production of nubuk leather (cow and calf leather) The leather which has been chrome-tanned in the usual manner is retanned with 6% (referred to the shaved weight of the leather) of the tanning agent described in Example 1 in powdered form and in a short liquor, deacidified and dyed, fat-liquored, dried and further dressed in the conventional way.

The leathers obtained according to Examples 10 to 13 are characterised by a very fine and level nap, as well as by brilliancy, fullness and levelness of the dyeing, and in the case of nubuk leather also by an extraordinary grain firmness.

EXAMPLE 14 Production of wool sheep or fur skins The skins prepared in the conventional manner are pickled with sodium chloride and sulphuric acid so that a final pH value of about 3 to 3.5 results, and subsequently tanned with 18% of the tanning agent described in Example 1, in the case of short-haired skins in a short liquor, in the case of long-haired skins in the usual liquor which should be as highly concentrated as possible and can be used for several batches. The skins are then neutralised in the usual manner, optionally, dyed, fat-liquored and further processed. The finished dressed skins are characterised by an excellent tear resistance, fastness to wet processing, perspiration and light, they are very soft and of good handle.

EXAMPLE Production of anilin kid leather in bright and light tints Kid pelts are pickled in the customary manner so that a final pH-value of about 2.5 to 3 results, and subsequently tanned with 12% (referred to the weight of the pelts) of the tanning agent described in Example 1, and according to the method given in Example 1. After shaving the leather is retanned with 25% (referred to the weight of the shaved material) of 33% basic technical chromium sulfate having a chromium oxide content of The tanned leather is than neutralised in usual manner, dyed, fat-liquored and finished.

The leather obtained is distinguished by a level and brilliant shade and by fine and firm grain and good handle.

EXAMPLE 16 Preparation of white leather Cow, calf, goat or sheep pelts are pickled in the customary manner so that a final pH-value of between 2.5-3.5 results. The liquor is than drained and the pickled material tanned with a mixture of 12% (referred to the weight of the pelts) of the tanning agent described in Example 1. 26% of a powdered, not astringent, lightfast auxiliary tanning agent (e.g., as described in Example 1 and prepared by condensing 1 mol of dihydroxydiphenylsulphone, 22.5 mols of formaldehyde and 1-1.25 mols of sodium sulfit), sluried with the same amount of water; the tanning is continued until the leather is completely tanned through, which lasts l4 hours, depending 8 on the thickness of the pelts. The further treatment of the tanned leather is carried out as mentioned in Example 1. The leather obtained is distinguished by its good white colour, the excellent plumpness and softness.

EXAMPLE 17 Production of shrunk leather with White cross section of the leather Completely delimed and well tawed cow, calf, goat or sheep pelts are well drained and drummed with 100% of water and 6% of sodium chloride for 5 minutes. 5-10% of a powdered, astringent, lightfast syntan (e.g., that described in Example 2 and prepared by condensation of 1 mol of dihydroxydiphenylsulphone, 22.5 mols of formaldehyde and 14.25 mols of sodium 'sulphite) are added. Before adding the syntan it is dissolved in three times the amount of water and 20% of its Weight of formic acid. Together with syntan 5% of the tanning agent described in Example 1 is added and the drumming continued for 2 hours. The liquor is then discharged and 7% of the tanning agent described in Example 1 added and the drumming continued until the leather is completely tanned through. The leather obtained is neutralised, fat-liquored and finished as usual for shrunk leather.

The leather is distinguished by its white colour, a thin shrunk grain, as well as its softness and plumpness.

We claim:

1. Process for tanning hides and leather by applying to the hides or leather tanning agents comprising a combination of zirconium, aluminum, and chromium salts, the proportion of these metal salts, based on the metal oxides ZrO :Al O :Cr O amounting respectively, to :5 to 50:2 to 30 parts by weight.

2. Process according to claim 1, wherein said combination comprises a mixed complex of zirconium, aluminum, and chromium salts, obtained by heating or dehydrating aqueous solutions thereof.

3. Process according to claim 1, wherein said tanning agents are applied in two sequential steps, the first of which comprises applying the zirconium salt and the second of which comprises applying the aluminum and chromium salts in the form of a simple mixture or a mixed complex.

4. Process according to claim 1, wherein said metal salts are the sulphates of zicronium, aluminum, and chromium.

5. Process according to claim 1, wherein said metal salts are in the form of cations of said metals and sulphate anions formed in situ during the tanning process.

6. Process according to claim 4, wherein said Zirconium sulphate is in combination with finely divided silica gel.

7. Process according to claim 1, wherein said tanning is carried out by applying to said hides or leather powders of a combination of zirconium, aluminum, and chromium salts in the absence of added water.

8. Process according to claim 1, wherein pickled pelts having a pH between 2.0 and 3.5 are treated, after removal of the pickle solution, with a highly concentrated solution or a powder of said tanning agents comprising zicronium, aluminum, and chromium salts.

9. Process according to claim 1, wherein pretanned chrome leather is retanned with said combination of the salts of zicronium, aluminum, and chromium.

10. Process according to claim 1, whereinsaid hides or leather, after being tanned with said combination of zirconium, aluminum, and chromium salts, are treated with mineral, synthetic, or vegetable tanning agents and fillers.

11. Process according to claim 1 wherein said proportion of metal salts is 100:10 to 20:3 to 8 parts by weight.

12. Process according to claim 8 wherein said solution or said powder is applied in two sequential steps, the first of which comprises applying the zicronium salt and the second of which comprises applying the aluminum and chromium salts in the form of a single mixture or a mixed complex.

References Cited UNITED STATES PATENTS 2,395,472 2/1946 Fernald et a1. 894.19 2,826,477 3/1958 Rau et a1. 8-94.26 2,997,363 8/1961 Pfirrman 894.26

l 0 OTHER REFERENCES Ramganathan et al., J our. Soc. Leather Trades Chemists, November 1958, pp. 357-359.

5 NORMAN G. TORCHIN, Primary Examiner.

DONALD LEVY, Assistant Examiner.

U.S. C1. X.R. 

1. PROCESS FOR TANNING HIDES AND LEATHER BY APPLYING TO THE HIDES OR LEATHER TANNING AGENTS COMPRISING A COMBINATION OF ZICRONIUM, ALUMINUM, AND CHROMIUN SALTS, THE PROPORTION OF THESE METAL SALTS, BASED ON THE METAL OXIDES ZRO2:AL2O3:CR2O3, AMOUNTING RESPECTIVELY, TO 100: 5 TO 50: 2 TO 30 PARTS BY WEIGHT. 